Nishith B. Desai

Integration of parabolic trough and linear Fresnel collectors for optimum design of concentrating solar thermal power plant

A concentrating solar power (CSP) plant with parabolic trough collector (PTC) using thermal oil as heat transfer fluid (HTF) is the most commercially established technology. On the other hand, linear Fresnel reflectors (LFRs) with direct steam generation (DSG) are developed and proposed as cheaper alternative to PTC systems. The optical efficiency of LFR systems is lower than that of PTC systems. Also low-cost LFR systems produce saturated steam, resulting in higher aperture area requirement compared to PTC-based CSP plants of the same capacity. In this paper, integration of parabolic trough and linear Fresnel collectors for an optimum design of a CSP plant is proposed. The integrated CSP plant configuration combines the advantages of conventional HTF-based PTC fields and DSG of LFR fields. Thermo-economic comparisons between PTC-based, LFR-based and integrated CSP plant configurations, without hybridization and storage, are presented in this paper. An approximate, but simple selection methodology for these configurations, based on the values of relative collector field costs per unit of energy gain and relative isentropic efficiency of turbines, is also proposed to generate selection diagram. This diagram helps in selecting optimum configuration for the CSP plant. The applicability of the proposed methodology is demonstrated through an illustrative case study. Detailed simulations are advisable in case of design point close to separation lines between different regions in the selection diagram.

Solar Thermal Process Heat

Recently, utilization of environmentally friendly renewable energy sources for power generation is increased. However, use of renewable energy sources for industrial process heat is still at an early stage of commercialization. The main emphasis had been on low-temperature domestic applications; however, medium-temperature process heat applications are also being supplied by solar technologies using concentrators. Solar heat for industrial processes has the technical potential to meet about 10% of the industrial energy demand globally (about 15 EJ) up to about 300°C. In this article, different solar thermal technologies are reviewed as well as different widely used process heat applications of solar thermal energy are briefly discussed along with the typical integration schematics. Before designing a system, one has to understand the different solar thermal technologies, process utility of the existing system, economics, etc. Apart from that actual performance of the solar thermal system differs compared to the instantaneous performance prediction used during the design stage. Issues in system designing and integration are also discussed.

Sustainability in Power Generation Systems

Conventional fossil fuels are the largest contributor of primary energy demand. Compared to conventional fossil fuel sources, renewable energy sources can be continually replenished and environmentally friendly and therefore, it is desirable to increase their usage with climate change perspective. In such policies, the unintended consequences of increased use of renewable energy sources in the long run, especially in terms of their effects on other natural resources (like, water, land, etc.), are typically ignored. Hydropower and biomass are more water intensive than others. Similarly, the production of ethanol and biomass requires large land areas. In this article, different power-generating technologies are studied in terms of different sustainability indicators. Due to strong interrelations of all components of the natural ecosystem, important sustainability indicators need to be studied to avoid failure of the whole system. It may be noted that different energy sources have been reported as a preferred option in the literature and this is due to uncertainties in factors, like performance parameters, sustainability indicators, region/place, and weighing. Therefore, the aggregate analysis-based method, for integration of different indicators, may play a significant role in selecting appropriate power generation technologies.